1. Field of the Invention
This invention relates to a brake band such as for use in the transmission of a vehicle (e.g., an automobile, an agricultural machine or construction equipment).
2. Related Background Art
In automatic transmissions, multiplate clutches, brake bands, etc. are used to effect speed change with an input element such as a gear train fixed and opened. Among these, the brake band is widely used because it has the characteristic that its braking force differs depending on the braking direction of a drum even if the same acting force is applied thereto. It also has the advantageous characteristic that it makes up-shift smooth.
As the construction of a brake band according to the prior art, there is one as shown, for example, in FIG. 7 of the accompanying drawings.
In FIG. 7, a brake band 7 is comprised of a strap 3 of curved thin steel plate having an adhesive agent applied thereto, brackets 4 and 4' coupled to the opposite ends of the strap 3, and a porous thin friction material (lining) 2 adhesively secured to the curved strap 3. The bracket 4 is an input side (apply side) bracket on which oil pressure force for operating the brake acts, and the bracket 4' is a support point side (anchor side) bracket.
In such a conventional brake band, there are sometimes provided an oil groove 5 and oil apertures 6 in the lining to improve the oil discharge characteristic between the drum and the lining in the binding process of the band brake. With prior structures of this type, speed change shock has been a significant problem. In particular, the discharge of the oil film intervening between the drum and the lining of the binding process of the band brake is low during the early stage of binding, with a resulting low friction characteristic. Toward the end of binding, however, the binding force suddenly increases, and this causes speed change shock. If the number of oil grooves and the number of (removing) discharge apertures are increased to further enhance the oil discharge performance, the surface pressure of the lining will increase and there will arise a problem in durability. In addition, if discharge apertures are formed in the brackets 4 and 4', the strength of the brackets may be reduced, and this can lead to damage of the brackets.